As molded articles for optical use, there is proposed a silicone rubber composition for optical use because a cured product having high transparency and high hardness can be obtained (JP-A 2008-101056, JP-A 2008-291124).
In applying a silicone rubber composition to optical use, there is a case where heat resistance is required in addition to transparency and hardness.
As a method of imparting heat resistance to a silicone rubber, there is known a method of blending a metal oxide powder.
In JP-B 43-3019, an organopolysiloxane rubber composition in which heat resistance is improved by blending an octanoate, chloride or acetate of cerium, lanthanum, neodymium, and the like into a silicone rubber.
In JP-A 60-163966, there is described a heat-resistant organopolysiloxane composition in which there was blended, into an organopolysiloxane as the component A, a reaction product obtained by subjecting an organopolysiloxane, a cerium carboxylate, a titanium or zirconium compound to heat treatment at a temperature of 150° C. or more as the component B. However, in any of Examples 1 to 3, there was produced a silicone oil or a dimethylpolysiloxane fluid.
In JP-B 43-3019, JP-A 60-163966, there is no description of transparency.
In WO-A1 2008/082001, there is described a thermally curable silicone rubber composition containing a cerium oxide powder in an amount of 0.001 to 10% by mass, and it is described that a total light transmittance at a thickness of 1 mm is 90% or more.